Electrodeposition of zinc-gold alloys



Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE HAROLD J. KERSTEN, OF CINCINNATI, OHIO, ASSIGNOR TO BOARD OF DIRECTORS OF THE UNIVERSITY OF CINCINNATI, OF CINCINNATI, OHIO ELECTRODEPOSITION OF ZINC-GOLD ALLOYS No Drawing.

My invention is addressed to the simultaneous electrodeposition of gold and zinc, with or without other metals, so as to pro duce virtual alloys thereof having. prop erties not hitherto available in the jewelry art, and to the production of articles coated with zinc-gold alloys. An object of my invention is to provide an electrolyte and a process for plating zinc-gold combinations, particularly a process which is controllable. Another object of my invention is the production of zinc-gold combinations of such homogeneous and dense form as to be unattacked by and to protect the base metal structure from attack by concentrated and dilute nitric acid,in other words the-production of new golds available to the jewelry art which will respond to the ordinary jewelers test for gold.

These and other objectsof my invention which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, I accomplish by that certain process and in that product of which I shall now describe a preferred embodiment.

Hitherto, so far as I am aware, virtual alloys consisting mainly or entirely of zinc and gold have not been produced electrolytically. 'It has been known that zinc and gold will alloy in various proportions giving metallic combinations of various colors; but these alloys, formed by melting the metals together, have invariably been lacking in malleability and'have been unfit for use in the art. By my invention I produce coatings of these alloys upon structures of base metal whereby they are made available for use. I have not investigated the physical properties of these coatings sufliciently to be able to say at this time .whether they are completely malleable, although they do not break upon flexing the base support upon which they are deposited.

In my invention I employ electrolytic baths, specific examples of which will be set forth hereinafter, which comprises salts of gold and zinc. -It is a problem to control selectively the deposition of the two metals in such baths because gold and zinc are so Application filed February 20, 1930. Serial No. 430,136.

widely separated in the electromotive series. Control is essential in the attainment of the objects of my invention, and is particularly important in determining the color of the resultant deposits. Alloys of gold and zinc may be made ranging from the yellow color of gold, through white gold colors to a lavender or lilac color which is particularly desirable and ornamental when used alone or in combination with yellow, white or green golds. The specific examples of my procedure which I shall now give are di rected to the production of a deposit of this desirable color, which is a metallic combination comprising about, 30% of zinc to 70% of gold. It will be understood that modifications may be made in my invention without departing from the spirit thereof.

Satisfactory deposits are produced in the following bath;

This bath is preferably used at 70 centigrade with an insoluble anode and a current density of one ampere per square centimeter. When used without agitation it will give beautiful lilac or lavender deposits.

The bath and the procedure given are suitable for the plat-ing or small articles such as watch cases and the like.

The effect of agitation is to change the color of the deposit somewhat. I explain this in the following way: even though the quantity of gold in the bath is small, it has a tendency to deposit. preferentially. It is probable that the first blush is very nearly pure gold, and would be yellow if of appreciable thickness. It shades off very quickly to the desired lavender or lilac color, probably through a white color, as theelectrolyte' around the cathode becomes depleted in gold ions. An equilibrium .is reached substantially at once which, in the absence of agitation, permits me to plate a deposit of the desired analysis under the conditions I have outlined. 'Agitation destroys this equilibrium, and increases the amount of ture, but also for trol the deposit selectively. It will be un-- derstood that in electroplating there are a very large number of variables such as current density,-temperature, agitation, the relative amounts of metal salts in the electrolyte, the eflective position of metals in the electromotive series as modified by the particular saltschosen, to say nothing of addition agents and other substances super-added to the bath. Not all of these have been completely investigated. In these specifications I set forth procedures suitable for the at tainment of the objects of my invention and have indicated at least one method. of modification to attain deposits of different proportions. It will be understood that modifications effected through the control of the variables mentioned or of other variables, do not fall outside the scope of my invention as hereinafter claimed.

By way of example, but without limitation, I have found that my preferred alloy may be plated, under the same conditions, from a bath of this composition:

Gold otassium cyanide (K1Eu(CN) 2.5 gm. Zinc potassium cyanide K Zn(CN) 10.0 gm. Water .1 liter I have also found that potassium or sodium zincate or other alkali zincates may be used instead of the zinc potassium cyanide.

It will be understood also that my process is useful not only for forming a complete wearing deposit upon a base metal strucflashing deposits of the same or other metals or. metallic combinations subsequent to the main bufling.

Having thus described my invention, what I claim as new and desire to secure by Let-.

ters Patent, is 1. A metal article bearing a surface coating of zinc and gold comprising approximately 30% zinc to of go1d.-

2. metal article having arr electrodeposited coating consisting of zinc and gold,

the said coating having a lilac color.

3. A homogenous electrodeposit consistviding an electrolyte containing a relatively small percentage of gold ions, a; relatively large percentage of zinc ions, and plating an electrodeposit therefrom upon a preformed article of base metal atapproximately one ampere per square centimeter of cathode sur- I face.

6. A process for producing useful coatings of zinc-gold metallic combinations.

which comprises providing an electrolyte containing a comparatively small percent age of gold ions, and a comparatively large percentage of zinc ions, together with current carrying ions of another metal, and plating therefrom upon a preformed metallic structure at a temperature around 70 centigrade, a current density around one ampere 15 grams of potassium cyanide, and 50 grams of potassium zinc cyanide to. 1 liter of water.

HAROLD J. KERSTEN.

ing solely of gold and zinc which resists the actiion ofconcentrated and dilute nitric acl electrodeposit of gold and zinc havmg a lilac color and comprising approximately 30% of zinc to? 0% of gold, the saidelectrodeposit being dense and homogeneous and not subject to attack by concentrated and dilute nitric acid. I

5. process of electroplating deposits of mac and gold of lilac color comprising pro- 

